The main theme of Plato’s allegory of the cave is that we humans tend not to understand the true reality of our world. We think that we understand what we are looking at and sensing in our world, but we really just perceive shadows of the true forms of the things that make up the world.

In the allegory of the cave, prisoners are chained in such a way that they can only see the back wall of their cave. They see shadows on the wall of the cave that are cast by objects being moved between a large fire behind them and the wall in front of them. Because they can only see the wall, they do not know that the objects on the wall are just shadows. They think the objects on the wall are the real things. For example, if they saw the shadow of a man, they would think that it was a real man because they had no way of knowing that it was just a shadow.

Plato is saying that, unless we become educated, we human beings are like the prisoners in the cave. We think that we understand the world around us. We think that the things we see and otherwise perceive are real. However, we are incorrect because the things that we perceive are mere shadows. There are true forms of everything that we think we perceive, but we cannot see those forms. In the allegory of the cave, Plato is trying to make us understand that we see shadows and we think they are the real thing. Thus, the main theme of the allegory is that we are ignorant about the true nature of reality.